InStyle's Summer Accessories 2010 Report features a sunglasses special, "Find Your Most Flattering Sunglasses!" It has the traditional advice for finding the best pair for faces of all shapes (heart, oval, long, wide, etc.).
Their recommended shades were pretty standard fare, but I do have a soft spot for Carrera 'Hippy' Sunglasses. Nordstrom has them for $98, but they're only $72 on buyeyeglasses.com.